Fix: paths api return empty if start and end with same vertex id

[zyxxoo]

paths api get and post method return same result

[codecov]

Codecov Report

Merging #1435 (b586d5b) into master (0e686ff) will increase coverage by 0.01%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master    #1435      +/-   ##
============================================
+ Coverage     62.21%   62.22%   +0.01%     
- Complexity     5856     5859       +3     
============================================
  Files           381      381              
  Lines         32135    32135              
  Branches       4504     4504              
============================================
+ Hits          19993    19997       +4     
+ Misses        10090    10089       -1     
+ Partials       2052     2049       -3     

Impacted Files	Coverage Δ	Complexity Δ
...a/com/baidu/hugegraph/backend/query/Condition.java	78.46% <0.00%> (ø)	32.00% <0.00%> (ø%)
...du/hugegraph/backend/tx/GraphIndexTransaction.java	81.27% <0.00%> (+0.23%)	204.00% <0.00%> (+1.00%)
...c/main/java/com/baidu/hugegraph/task/HugeTask.java	69.84% <0.00%> (+0.30%)	82.00% <0.00%> (+1.00%)
...va/com/baidu/hugegraph/task/ServerInfoManager.java	70.78% <0.00%> (+0.56%)	51.00% <0.00%> (+1.00%)

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